Several different methods and devices have been suggested and used in practice for causing an unmanned vehicle (automatically guided vehicle) to move from one destination to another on a factory floor or the like along a predetermined path consisting of a wire or loop of a suitable material disposed along the path. Such a wire may be an induction line, an optically reflective line etc. The vehicle is provided with suitable means for following the wire and for correcting deviations from the predetermined path. Optical wire-tracking systems are disclosed in e.g. GB No. 1,500,970 and DE No. 2,258,764.
Wire guidance systems of the above-mentioned type however suffer from several drawbacks. First, it is often a costly and time-consuming procedure to arrange a new wire or to modify a path already arranged. Secondly, relatively complicated sensor and control devices are required on each vehicle for sensing the wire and guiding the vehicle, which increases costs especially in larger plants. Thirdly, a wire or the like disposed directly on a floor surface may be damaged by external influence or, in the case of an optically reflective wire, may become inoperative because of dust, dirt or the like on the same. Fourthly, such a wire guidance system does not provide an overall survey of all the vehicles in a system, but the wire is used only for guiding the vehicle from one destination to another.